Maintaining packet data connectivity in a wireless communications network

ABSTRACT

Techniques for maintaining packet data connectivity in a wireless communications network are presented. A mobile station detects a change from a first packet control function (PCF) to a second PCF. The first PCF is connected to a first packet data service node (PDSN). The second PCF is connected to a second PDSN. The mobile station consults a database configured to map at least one previously visited PCF to a servicing PDSN. Based at least in part on the consulting, the mobile station observes one from among a plurality of predetermined origination patterns, wherein an origination pattern defines origination functions to be performed by the mobile station. As such, zombie PPP and mobile IP instances may be detected and handled.

RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional ApplicationNo. 60/333,642 filed on Nov. 26, 2001.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates generally to the field of wirelesscommunications. More specifically, this invention relates to novel andimproved techniques for maintaining packet data connectivity in awireless communications network.

[0004] 2. Description of Related Art

[0005] Recent innovations in wireless communications andcomputer-related technologies, as well as the unprecedented growth ofInternet subscribers, have paved the way for mobile computing. In fact,the popularity of mobile computing has placed greater demands on thecurrent Internet infrastructure to provide mobile users with moresupport. A crucial part of meeting these demands and providing userswith the necessary support is the use of Code Division Multiple Access(CDMA) technology.

[0006] CDMA is a digital radio-frequency (RF) channelization technique.CDMA2000 is a recently promulgated CDMA standard. Release 0 of CDMA2000is introduced in TIA/EIA/IS2000.1-2, entitled “INTRODUCTION TO CDMA2000SPREAD SPECTRUM SYSTEMS, RELEASE 0-ADDENDUM 2,” published in April 2001and herein incorporated by reference. Release A of CDMA2000 isintroduced in IS-2000-A, entitled “INTRODUCTION TO CDMA2000 STANDARDSFOR SPREAD SPECTRUM SYSTEMS,” published in June 2000 and hereinincorporated by reference.

[0007] In various wireless communications system architectures, a mobilestation wirelessly connects to a radio access network (RAN) thatservices a given area. Each RAN includes a base station controller(BSC), which includes a packet control function (PCF). The PCF acts asan interface to a packet data service node (PDSN), which in turn acts asan interface to IP (Internet Protocol) networks.

[0008] When a mobile station roams into an area serviced by a RAN, thePCF or PDSN may change. According to the CDMA2000 specification, upondetecting a change in PCFs, the mobile sends an Enhanced OriginationMessage (EOM) to the RAN indicating that the mobile requiresconnectivity with a PDSN associated with the RAN. A change in PDSNsgenerally requires the mobile to negotiate a PPP (Point-to-PointProtocol) session with the new PDSN and perform mobile IP registration.

[0009] More particularly, after establishing and maintaining a PPPsession with a first PDSN in a first service area, a mobile station maygo dormant to conserve resources. The mobile may then venture into asecond service area associated with a second PDSN, negotiate PPP, andregister mobile IP. The mobile may again go dormant and, as the mobiletravels, it may return back to the first service area, where a PPPinstance—a “zombie instance”—associated with the earlier visit is stilloperative.

[0010] In CDMA2000 Release A systems, a mobile station sends wirelessIDs of the previous PCF in the EOM. Such systems can determine whetherthe mobile emerging from dormancy mode had ventured into another PDSNservice area during the period of dormancy. If the new PCF is the sameas the previous PCF, then the traffic channel is not brought up.Otherwise, the traffic channel is brought up, PPP resynchronizes, andmobile IP re-registers. However, the EOM in CDMA2000 Release 0 systemsdoes not provide for sending of the wireless IDs of the previous PCF. Assuch, CDMA2000 Release 0 systems cannot identify and handle zombie PPPinstances.

SUMMARY OF THE INVENTION

[0011] Novel techniques consistent with the principles of the presentinvention, as embodied and broadly described herein, are presented formaintaining packet data connectivity in a wireless communicationsnetwork. In one embodiment, a mobile station detects a change from afirst packet control function (PCF) to a second PCF. The first PCF isconnected to a first packet data service node (PDSN). The second PCF isconnected to a second PDSN. The mobile station consults a databaseconfigured to map at least one previously visited PCF to a servicingPDSN. Based at least in part on the consultation, the mobile stationobserves one from among a plurality of predetermined originationpatterns, wherein an origination pattern defines origination functionsto be performed by the mobile station.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 illustrates a wireless communications system architecture.

[0013]FIG. 2 is a high-level block diagram of a mobile station accordingto an embodiment of the present invention.

[0014]FIG. 3 illustrates exemplary contents of a database according toan embodiment of the present invention.

[0015]FIG. 4 is a high-level functional flow diagram of a processaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0016] The following detailed description refers to the accompanyingdrawings that illustrate embodiments of the present inventions. Otherembodiments are possible and modifications may be made to theembodiments without departing from the spirit and scope of theinvention. Therefore, the following detailed description is not meant tolimit the invention. Rather, the scope of the invention is defined bythe appended claims.

[0017] It will be in many different embodiments of software, firmware,and hardware in the entities illustrated apparent to one of ordinaryskill in the art that the embodiments as described below may beimplemented in the figures. The actual software code or specializedcontrol hardware used to implement the present invention is not limitingof the present invention. Thus, the operation and behavior of theembodiments will be described without specific reference to the actualsoftware code or specialized hardware components. The absence of suchspecific references is feasible because it is clearly understood thatartisans of ordinary skill would be able to design software and controlhardware to implement the embodiments of the present invention based onthe description herein with only a reasonable effort and without undueexperimentation.

[0018] Moreover, the processes associated with the presented embodimentsmay be stored in any storage device, such as, for example, a computersystem (nonvolatile) memory, an optical disk, magnetic tape, or magneticdisk. Furthermore, the processes may be programmed when the computersystem is manufactured or via a computer-readable medium at a laterdate. Such a medium may include any of the forms listed above withrespect to storage devices and may further include, for example, acarrier wave modulated, or otherwise manipulated, to convey instructionsthat can be read, demodulated/decoded and executed by a computer.

[0019] Embodiments of the present invention provide techniques for amobile station to maintain packet connectivity in a wirelesscommunications network. A mobile station connects to the Internet orother network via a packet control function (PCF) in a radio accessnetwork (RAN). The PCF is associated with a packet data service node(PDSN) that acts as a foreign agent. The mobile station maintains adatabase that maps identifiers of each PCF visited by the mobile stationto the IP address of the associated PDSN. The PDSN IP address may beobtained by the mobile station via a mobile IP agent advertisementmessage broadcast by the PDSN. The mobile station detects a change inPCFs, which may result from movement of the mobile station into anotherservice area. The new PCF has an associated new PDSN.

[0020] The mobile station consults a database to determine how the newPCF and PDSN are related to the previous PCF and PDSN. In particular,the new PCF may have been previously visited by the mobile station, andthe new PDSN may be the same as the previous PDSN. Based on the databaseconsultation, the mobile station performs various origination functions.For instance, origination functions may include setting the DRS bit inan Enhanced Origination Message (EOM) to one or zero, renegotiating aPoint-to-Point Protocol (PPP) session, or sending a mobile IP agentsolicitation message.

[0021] Thus, the mobile station's own origination functions may ensurethat zombie sessions do not precipitate problems in wirelesscommunications systems.

[0022] CDMA was first defined in the Telecommunications IndustryAssociation/Electronics Industries Association Interim Standard-95(TIA/EIA IS-95), entitled “MOBILE STATION-BASE STATION COMPATIBILITYSTANDARD FOR DUAL-MODE WIDEBAND SPREAD SPECTRUM CELLULAR SYSTEM,”published in July 1993 and herein incorporated by reference. Recentlypromulgated CDMA standards include TIA/EIA/IS-856, entitled “CDMA2000,HIGH RATE PACKET DATA AIR INTERFACE SPECIFICATION,” published inNovember 2000 and herein incorporated by reference. TIA/EIA/IS-856 isalso known as 1xEV. Wireless communications systems employing CDMAtechnology assign a unique code to communication signals and spreadthese communication signals across a common (wideband) spread spectrumbandwidth.

[0023] Other support is made possible by applying various well-knownprotocols to control, manage, or otherwise facilitate different aspectsof wireless communications. For example, the lifeblood of the Internetinfrastructure, the Internet Protocol (IP), has been incorporated inmany wireless communication services to accommodate packet-orientedservices. The IP protocol is a network layer protocol that encapsulatesdata into IP packets for transmission. In particular, the IP protocolspecifies the addressing and routing of packets (datagrams) between hostcomputers. Version 4 of the IP protocol (“IPv4”) is defined in RequestFor Comments 791 (RFC 791), entitled “INTERNET PROTOCOL DARPA INTERNETPROGRAM PROTOCOL SPECIFICATION,” published September 1981, and hereinincorporated by reference.

[0024] Another well-known protocol incorporated in wirelesscommunications systems is the Point-to-Point Protocol (PPP) protocol,which provides, inter alia, Internet access. The PPP protocol isdescribed in detail in Request for Comments 1661 (RFC 1661), entitled“THE POINT-TO-POINT PROTOCOL (PPP),” published July 1994 and hereinincorporated by reference. The PPP protocol specifies a method fortransporting multi-protocol datagrams over point-to-point links.

[0025] Ideally, mobile computing should provide a user with seamless andtransparent Internet access regardless of time and the user's currentpoint of attachment. Request For Comments 2002 (RFC 2002), entitled “IPMOBILITY SUPPORT,” dated October 1996 and herein incorporated byreference, specifies protocol techniques to achieve the transparentforwarding of IP packets to mobile terminals regardless of theirparticular point of attachment. When the mobile terminal detects that itis no longer operating within its “home” IP network but is visiting a“foreign” IP network, it obtains a foreign network “care-of” addresswhich provides forwarding information necessary to route IP packets toits current point of attachment. This care-of address may be profferedby an agent on the foreign network (“Foreign Agent”)—e.g., a router,such as a packet data service node (PDSN)—through its AgentAdvertisement message. Mobile IP techniques require that the mobileterminal send a Registration-Request message to a “Mobility Agent” inorder to register a desired care-of address. This Mobility Agent mayeither be a “Home Agent” (i.e., a router in the terminal's home network)or the “Foreign Agent.” After registration, the mobile terminal andMobility Agent may negotiate a PPP session, thus ensuring that theirconfiguration parameters for the PPP link are the same.

[0026]FIG. 1 illustrates a wireless communications system architecture100 in which mobile terminal equipment, TE device 102 (e.g., a mobileterminal, laptop, or palmtop computer), wirelessly connects to either ofradio access networks (RANs) 130, 131 via a wireless communicationsdevice, MT 104. TE device 102 and MT device 104, which areelectronically coupled, may be integrated into a single unit or may beseparated out as in an installed mobile phone unit in which a laptop isTE device 102 and the transceiver is MT device 104. The combination ofTE device 102 and MT device 104, whether integrated or separate, is alsoreferred to as a mobile node, and is denoted in FIG. 1 as mobile station(MS) 103.

[0027] Each RAN 130, 131 includes a base station controller (BSC) 106,107, and associated base station transceivers (BSTs) (not shown), and aMobile Switching Center (MSC) 125, 126. BSC 106, 107 includes a packetcontrol function (PCF) 120, 121. PCF 120, 121 acts as an interface to apacket data service node (PDSN), such as PDSN 140A or 140B. PDSN 140A,140B may be configured as a router that acts as an interface to IPnetworks 145A, 145B, such as the Internet and intranets. Each PDSN 140A,140B is a mobility anchor point for a mobile node, such as MS 103,roaming outside of a home network. Multiple PCFs may connect to aparticular PDSN. A particular PCF may connect to multiple PDSNs. EachPDSN has a unique IP address.

[0028] Various roaming situations involve MS 103. First, in a PCF-to-PCFhandoff situation (intra-PDSN), MS 103 moves from one BSC to anotherBSC, that is, MS 103 moves from one PCF to another PCF, wherein bothBSCs (PCFs) are connected to the same PDSN. This type of handoff may notrequire the renegotiation of the PPP session between MS 103 and the PDSNbecause the PDSN can reassociate the PPP state of MS 103 with the newBSC. Second, in a PDSN-to-PDSN handoff situation (inter-PDSN), MS 103roams into a new network with a different PDSN. As such, the mobile nodeis required to establish a new PPP link to the new PDSN and then performmobile IP registration again.

[0029] As shown in FIG. 1, PDSN 140A is associated with PCF 120 and PDSN140B is associated with PCF 121. If MS 103 enters the service area ofRAN 130, MS 103 may bring up a PPP session with PDSN 140A. After apredetermined interval of time, MS 103 may become dormant. That is, atsome point MS 103 may release a traffic channel to conserve over-the-airresources while maintaining PPP session connectivity with PDSN 140A.

[0030] MS 103 may then move from the service area of PDSN 140A to theservice area of PDSN 140B. According to the CDMA2000 specification, upondetecting a change in PCFs, MS 103 sends an Enhanced Origination Message(EOM) to RAN 131 indicating that MS 103 requires connectivity with PDSN140B. Because PDSN 140B does not have a PPP session for MS 103, PDSN140B brings up a traffic channel and initiates PPP negotiation betweenPDSN 140B and MS 103. The EOM includes DRS (Data-Ready-Send) bitinformation. Accordingly, when the DRS bit equals 0, MS 103 conveys thatit has no application data to send. Conversely, when the DRS bit equals1, MS 103 conveys that it has application data to send.

[0031] After establishing and maintaining a PPP session with PDSN 140B,MS 103 may again go dormant to conserve resources. If MS 103 moves backto the service area of PDSN 140A, MS 103 detects a change in PCFs andsends an origination message to RAN 130 with DRS equal to 0. Because nomechanism exists to notify PDSN 140A that MS 103 ventured into theservice area of PDSN 140B, PDSN 140A does not renegotiate the PPPsession between PDSN 140A and MS 103. As such, the RAN-PDSN (R-P)interface between PDSN 140B and MS 103 is still operative even though MS103 is in the service area of PDSN 140A. Thus, the PPP instanceassociated with the earlier venture of MS 103 into the service area ofPDSN 140A is a so-called “zombie” PPP instance of MS 103 in PDSN 140A.

[0032] In CDMA2000 Release A systems, the mobile sends wireless IDs ofthe previous PCF in the EOM. Thus, such systems can determine whether MS103 emerging from dormancy mode had ventured into another PDSN servicearea. If the new PCF is the same as the previous PCF, then the trafficchannel is not brought up. Otherwise, the traffic channel is brought up,PPP resynchronizes, and mobile IP reregisters. The EOM in CDMA2000Release 0 systems does not provide for sending of the wireless IDs ofthe previous PCF. As such, CDMA2000 Release 0 systems cannot identifyand handle zombie PPP instances.

[0033]FIG. 2 is a high-level block diagram of a mobile station (MS) 200according to an embodiment of the present invention. MS 200 includes aPCF change detection mechanism 210, a database consulting mechanism 220,an origination pattern response mechanism 230, and a database 240. It isto be appreciated that entities within MS 200 may be incorporated withina TE device or MT device, as described generally above with respect toFIG. 1. Further, database 240 need not reside on MS 200 in otherembodiments if MS 200 can access database 240. In some embodiments, PCFchange detection mechanism 210 and database consulting mechanism 220 maycomprise one module.

[0034] PCF change detection mechanism 210 detects when MS 200 has movedfrom an area serviced by a first PCF to an area serviced by a secondPCF. In CDMA2000 systems, for example, a PCF may be identified uniquelyby a set of wireless network IDs. In particular, CDMA2000 provides for asystem identifier (SID), network identifier (NID), and packet zoneidentifier (PZID). Together, an SDINID/PZID combination, broadcasted bythe PCF in a paging channel, uniquely identifies each PCF, thusassisting MS 200 in determining whether MS 200 has ventured into adifferent service area. In some embodiments, PCF change detectionmechanism 210 may compare the broadcasted wireless network IDs towireless IDs recently stored in MS 200, such as in database 240 oranother nonvolatile or volatile memory. Therefore, when the compared IDsdo not match, PCF change detection mechanism 210 may register a changein PCFs, which would correspond to movement by MS 200 into a new servicearea.

[0035]FIG. 3 illustrates exemplary contents of database 240 in MS 200according to an embodiment of the present invention. As shown, database240 maps wireless IDs of each PCF visited by MS 200 to the IP address ofthe PDSN corresponding to the visited PCF. The IP address of each PDSNmay be provided by an agent advertisement sent by a PDSN, or within thecontext of a PPP-IPCP negotiation. IPCP is a part of a family of networkcontrol protocols included in the PPP protocol and described in Requestfor Comments (RFC) 1332, “THE PPP INTERNET PROTOCOL CONTROL PROTOCOL(IPCP),” published in May 1992 and herein incorporated by reference.Database 240 may maintain a history of such PCF wireless ID to PDSN IPaddress mappings. In some embodiments, older records in database 240 maybe occasionally deleted to conserve storage capacity.

[0036] Database consulting mechanism 220 in FIG. 2 may consult database240 to make various determinations. For instance, database consultingmechanism 220 may determine, based on the mappings: (1) whether the newPCF was previously visited by MS 200 and the PDSN associated with thenew PCF is the same PDSN as the most recently visited PDSN; (2) whetherthe new PCF was previously visited by MS 200 and the new PDSN differsfrom the most recently visited PDSN; and (3) whether the new PCF was notpreviously visited by MS 200. Specifically, database consultingmechanism 220 may compare the wireless IDs of the new PCF with wirelessIDs of previously visited PCFs that are stored in database 240. Further,database consulting mechanism 220 may compare the IP address of the newPDSN with the stored IP address of the most recently visited PDSN.

[0037] Origination pattern response mechanism 230 in MS 200 causes MS200 to observe predetermined origination patterns. In an exemplaryimplementation, origination patterns define specific originationfunctions that MS 200 should perform when sending Enhanced OriginationMessages (EOMs). Origination pattern response mechanism 230 selectsparticular origination patterns based in part upon the consultation ofdatabase 240 by database consulting mechanism 220. More specifically,because database 240 provides a history of PCF and PDSN mappings, MS 200may accurately and efficiently take steps to ensure that zombieinstances at PDSNs previously visited and then returned thereto are notmistaken as valid PPP sessions. Origination functions may include anynumber of exemplary actions, such as sending an agent solicitation,sending an EOM with the DRS bit appropriately set to 0 or 1,reregistering mobile IP, or renegotiating PPP.

[0038]FIG. 4 is a high-level functional flow diagram of a process 400according to an embodiment of the present invention. Herein, the term“previous” PDSN denotes a PDSN to which a mobile station is connectedimmediately before a change in PCFs. In task 401, a MS 200 that isconnected to a PCF and associated PDSN enters dormant mode. In task 405,process 400 checks whether the PCF changed, that is, whether MS 200 hasmoved into a new service area. If the PCF has not changed, then process400 remains at task 405 to continue the checking. If the PCF changes toa new PCF, then process 400 consults a database in task 410.

[0039] In task 415, process 400 determines whether the new PCF waspreviously visited by MS 200 and the new PCF is connected to the samePDSN as the previous PDSN. If so, in task 420, the dormant MS 200reoriginates with the DRS bit of the EOM set to 0, thereby indicating tothe RAN that MS 200 requires connectivity with the previous PDSN; an R-P(RAN-PDSN) link then can be established between the new PCF and theprevious PDSN. Because MS 200 is already registered with the new PDSN, aPPP state and a mobile IP binding exist. Thus, traffic need not begenerated for either of these protocols. The R-P link is established intask 425 and process 400 concludes.

[0040] If, in task 415, the determination is negative, then process 400proceeds to task 430. In task 430, process 400 determines whether thenew PCF was previously visited and the new PCF uses a different PDSNthan the previous PDSN. If so, then the point of attachment of MS 200 tothe Internet has changed because the PDSN has changed. As such, thedormant MS 200 originates with the DRS bit of the EOM set to 1 (task435). MS 200 renegotiates PPP (task 440) because there is a possibilitythat the new PDSN has a PPP state for MS 200—e.g., a dormant state—thatmay have been negotiated with different options than were negotiatedwith the previous PDSN. For instance, the new and previous PDSN may berespectively associated with different vendors or may have beenconfigured differently. MS 200 then re-registers mobile IP (task 445).Process 400 then concludes.

[0041] If the determination in task 430 is negative, then process 400proceeds to task 450, wherein it is noted that the new PCF has not beenvisited before. The dormant MS 200 originates with the DRS bit set to 1(task 488). In task 489, MS 200 waits for the traffic channel to comeup. Once the traffic channel comes up, MS 200 sends an agentsolicitation (task 490), without restarting PPP, to attempt to ascertainthe IP address of the PDSN associated with the new PCF. This approachmay be considered a conservative one, for MS 200 does not know whetherthe PDSN has been visited before. If MS 200 has never before visited thenew PDSN (task 492), there is no dormancy state for MS 200 at the newPDSN. PPP renegotiation is initiated by the PDSN in task 494, mobile IPis re-registered in task 495, and process 400 concludes. An agentsolicitation can be sent in task 490 if the network is set up such thatACCM/PFC/AFC options do not differ among various PDSNs. If the optionsdiffer, then MS 200 needs to renegotiate PPP.

[0042] If MS 200 has visited the new PDSN before (task 492), then intask 460, MS 200 checks for a response from the PDSN. If there is noresponse from the PDSN in task 460, then MS 200 may renegotiate PPP(task 465) and re-register mobile IP (task 466), and process 400 thenconcludes. The failure of the PDSN to respond may indicate that therespective PPP options of MS 200 and the PDSN are different, causingagent solicitation packets to be discarded.

[0043] If the PDSN responds in task 460, such as via an agentadvertisement, then MS 200 receives the advertised IP address of thePDSN in task 467. Process 400 consults a database in task 470 to checkthe IP address of the previous PDSN. In task 475, process 400 determineswhether the IP address of the new PDSN is identical to the IP address ofthe previous PDSN. If so, then PPP renegotiation is not needed (task480), and process 400 concludes. If the respective IP addresses differin task 475, then PPP is renegotiated in task 485 to ensure that the PPPoptions of MS 200 and the PDSN are the same, mobile IP is re-registeredin task 486, and process 400 concludes.

[0044] In another embodiment (not shown), an agent solicitation is notsent by MS 200 in task 490. Instead, PPP is renegotiated. Then, if thePDSN is a different PDSN than the previous PDSN, mobile IP isre-registered.

[0045] In another embodiment (not shown), MS 200 is on the trafficchannel, that is, MS 200 is not dormant. MS 200 returns to aPDSN/Foreign Agent that has a zombie PPP instance for MS 200. If thePDSN/Foreign Agent sends packets to the Home Agent, the PDSN/ForeignAgent may receive a return message, analogous to an ICMP redirect, whichindicates that a binding no longer exists between the home address andcare-of address of MS 200. Based on this return message, thePDSN/Foreign Agent can terminate the session with MS 200 and reinitiatea new session.

[0046] In another embodiment (not shown), MS 200 is on the trafficchannel. The traffic channel may send an In Traffic Systems ParametersMessage that conveys PCF SID/NID/PZID wireless IDs. If MS 200 detects achange in PCFs, then MS 200 may follow the tasks of process 400,beginning with task 410, in order to originate appropriately so as toclose zombie PPP sessions.

[0047] The foregoing description of the preferred embodiments isprovided to enable any person skilled in the art to make or use thepresent invention. Various modifications to these embodiments arepossible, and the generic principles presented herein may be applied toother embodiments as well. For instance, the teachings herein may applygenerally to protocols wherein a mobile station performs originationfunctions, such as protocols related to PPP renegotiation and mobile IPreregistration, as well as analogous protocols. In particular, thedetailed embodiments presented above can be designed to support one ormore wireless communication standards, including the following CDMAstandards: IS-95, IS-98, CDMA2000, W-CDMA, some other CDMA standard or acombination thereof. These standards are known in the art and are notdiscussed in detail herein.

[0048] Further, the invention may be implemented in part or in whole asa hardwired circuit, as a circuit configuration fabricated into anapplication-specific integrated circuit, or as a firmware program loadedinto non-volatile storage or a software program loaded from or into adata storage medium as machine-readable code, such code beinginstructions executable by an array of logic elements such as amicroprocessor or other digital signal processing unit.

[0049] As such, the present invention is not intended to be limited tothe embodiments shown above but rather is to be accorded the widestscope consistent with the principles and novel features disclosed in anyfashion herein.

What is claimed is:
 1. A method of maintaining packet data connectivityin a wireless communications network, comprising: detecting a changefrom a first packet control function (PCF) to a second PCF, the firstPCF corresponding to a first packet data service node (PDSN), the secondPCF corresponding to a second PDSN; consulting a database configured tomap at least one previously visited PCF to a servicing PDSN; andobserving at least one origination pattern from among a plurality ofpredetermined origination patterns based at least in part on theconsulting, wherein an origination pattern defines origination functionsto be performed by a mobile station in order to maintain connectivitywithin the network.
 2. The method of claim 1, wherein the consultingcomprises at least one of: determining whether the second PCF waspreviously visited by the mobile station and the second PDSN is the sameas the first PDSN; determining whether the second PCF was previouslyvisited by the mobile station and the second PDSN differs from the firstPDSN; and determining whether the second PCF was not previously visitedby the mobile station.
 3. The method of claim 1, wherein the originationfunctions include at least one of reregistering mobile IP andrenegotiating PPP (Point-to-Point Protocol).
 4. The method of claim 1,wherein the origination functions include sending an EnhancedOrigination Message wherein a data-ready-send (DRS) bit is set to one orzero.
 5. The method of claim 1, wherein the origination functionsinclude sending an agent solicitation to solicit a response from thesecond PDSN.
 6. The method of claim 5, wherein the origination functionsfurther include terminating or renegotiating PPP (Point-to-PointProtocol) if no response to the agent solicitation is received by themobile station from the second PDSN.
 7. The method of claim 5, whereinthe origination functions further include consulting the database todetermine whether an IP address received from the second PDSN inresponse to the agent solicitation matches an IP address of the firstPDSN stored in the database.
 8. The method of claim 7, wherein theorigination functions further include renegotiating PPP (Point-to-PointProtocol) if the received P address matches the IP address of the firstPDSN.
 9. A method of maintaining packet data connectivity in a wirelesscommunications network, comprising: sending, by a packet data servicenode (PDSN) to a home agent of a mobile station, at least one packet,wherein the PDSN has an open session with the mobile station, the opensession comprising a zombie session; receiving, by the PDSN from thehome agent, a return message; and terminating the open session, by thePDSN, based at least in part on the received return message.
 10. Themethod of claim 9, wherein the return message indicates nonexistence ofa binding for the mobile station.
 11. The method of claim 9, furthercomprising reinitiating, by the PDSN, a session with the mobile station.12. The method of claim 9, wherein the mobile station is on a trafficchannel.
 13. An apparatus for maintaining packet data connectivity in awireless communications network, comprising: means for detecting achange from a first packet control function (PCF) to a second PCF, thefirst PCF corresponding to a first packet data service node (PDSN), thesecond PCF corresponding to a second PDSN; means for consulting adatabase configured to map at least one previously visited PCF to aservicing PDSN; and means for observing at least one origination patternfrom among a plurality of predetermined origination patterns based atleast in part on the consulting, wherein an origination pattern definesorigination functions to be performed by a mobile station in order tomaintain connectivity within the network.
 14. A device comprising: amemory; and a digital signal processing unit coupled to the memory andconfigured to: detect a change from a first packet control function(PCF) to a second PCF, the first PCF corresponding to a first packetdata service node (PDSN), the second PCF corresponding to a second PDSN;consult a database configured to map at least one previously visited PCFto a servicing PDSN; and observe at least one origination pattern fromamong a plurality of predetermined origination patterns based at leastin part on the consulting, wherein an origination pattern definesorigination functions to be performed by a mobile station in order tomaintain connectivity within a wireless communications network.
 15. Thedevice of claim 14, wherein the consulting comprises at least one of:determining whether the second PCF was previously visited by the mobilestation and the second PDSN is the same as the first PDSN; determiningwhether the second PCF was previously visited by the mobile station andthe second PDSN differs from the first PDSN; and determining whether thesecond PCF was not previously visited by the mobile station.
 16. Thedevice of claim 14, wherein the origination functions include at leastone of reregistering mobile IP and renegotiating PPP (Point-to-PointProtocol).
 17. The device of claim 14, wherein the origination functionsinclude sending an Enhanced Origination Message wherein adata-ready-send (DRS) bit is set to one or zero.
 18. The device of claim14, wherein the origination functions include sending an agentsolicitation to solicit a response from the second PDSN.
 19. The deviceof claim 18, wherein the origination functions further includeterminating or renegotiating PPP (Point-to-Point Protocol) if noresponse to the agent solicitation is received by the mobile stationfrom the second PDSN.
 20. The device of claim 18, wherein theorigination functions further include consulting the database todetermine whether an IP address received from the second PDSN inresponse to the agent solicitation matches an IP address of the firstPDSN stored in the database.
 21. The device of claim 20, wherein theorigination functions further include renegotiating PPP (Point-to-PointProtocol) if the received IP address matches the IP address of the firstPDSN.
 22. An apparatus for maintaining packet data connectivity in awireless communications network, comprising: a change detectionmechanism configured to detect a change from a first packet controlfunction (PCF) to a second PCF, the first PCF corresponding to a firstpacket data service node (PDSN), the second PCF corresponding to asecond PDSN; a database configured to map at least one previouslyvisited PCF to a servicing PDSN; a database consulting mechanismconfigured to consult the database; and an origination pattern responsemechanism configured to cause a mobile station to observe at least oneorigination pattern from among a plurality of predetermined originationpatterns, based at least in part on the consulting, wherein anorigination pattern defines origination functions to be performed by themobile station in order to maintain connectivity within the network. 23.The apparatus of claim 22, wherein the database consulting mechanism isconfigured to determine at least one of: whether the second PCF waspreviously visited by the mobile station and the second PDSN is the sameas the first PDSN; whether the second PCF was previously visited by themobile station and the second PDSN differs from the first PDSN; andwhether the second PCF was not previously visited by the mobile station.24. The apparatus of claim 22, wherein the origination functions includeat least one of reregistering mobile IP and renegotiating PPP(Point-to-Point Protocol).
 25. The apparatus of claim 22, wherein theorigination functions include sending an Enhanced Origination Messagewherein a data-ready-send (DRS) bit is set to one or zero.
 26. Theapparatus of claim 22, wherein the origination functions include sendingan agent solicitation to solicit a response from the second PDSN. 27.The apparatus of claim 26, wherein the origination functions furtherinclude terminating or renegotiating PPP (Point-to-Point Protocol) if noresponse to the agent solicitation is received by the mobile stationfrom the second PDSN.
 28. The apparatus of claim 26, wherein theorigination functions further include consulting the database todetermine whether an IP address received from the second PDSN inresponse to the agent solicitation matches an IP address of the firstPDSN stored in the database.
 29. The apparatus of claim 28, wherein theorigination functions further include renegotiating PPP (Point-to-PointProtocol) if the received IP address matches the IP address of the firstPDSN.
 30. A computer-readable medium encoded with a plurality ofprocessor-executable instructions for: detecting a change from a firstpacket control function (PCF) to a second PCF, the first PCFcorresponding to a first packet data service node (PDSN), the second PCFcorresponding to a second PDSN; consulting a database configured to mapat least one previously visited PCF to a servicing PDSN; and observingat least one origination pattern from among a plurality of predeterminedorigination patterns based at least in part on the consulting, whereinan origination pattern defines origination functions to be performed bya mobile station in order to maintain connectivity within a wirelesscommunications network.
 31. The computer-readable medium of claim 30,wherein the consulting comprises at least one of: determining whetherthe second PCF was previously visited by the mobile station and thesecond PDSN is the same as the first PDSN; determining whether thesecond PCF was previously visited by the mobile station and the secondPDSN differs from the first PDSN; and determining whether the second PCFwas not previously visited by the mobile station.
 32. Thecomputer-readable medium of claim 30, wherein the origination functionsinclude at least one of reregistering mobile IP and renegotiating PPP(Point-to-Point Protocol).
 33. The computer-readable medium of claim 30,wherein the origination functions include sending an EnhancedOrigination Message wherein a data-ready-send (DRS) bit is set to one orzero.
 34. The computer-readable medium of claim 30, wherein theorigination functions include sending an agent solicitation to solicit aresponse from the second PDSN.
 35. A mobile station for maintainingpacket data connectivity in a wireless communications network, themobile station configured to: detect a change from a first packetcontrol function (PCF) to a second PCF, the first PCF corresponding to afirst packet data service node (PDSN), the second PCF corresponding to asecond PDSN; consult a database configured to map at least onepreviously visited PCF to a servicing PDSN; and observe at least oneorigination pattern from among a plurality of predetermined originationpatterns based at least in part on the consulting, wherein anorigination pattern defines origination functions to be performed by themobile station in order to maintain connectivity within the network. 36.The mobile station of claim 35, wherein the consulting comprises atleast one of: determining whether the second PCF was previously visitedby the mobile station and the second PDSN is the same as the first PDSN;determining whether the second PCF was previously visited by the mobilestation and the second PDSN differs from the first PDSN; and determiningwhether the second PCF was not previously visited by the mobile station.37. The mobile station of claim 35, wherein the origination functionsinclude at least one of reregistering mobile IP and renegotiating PPP(Point-to-Point Protocol).
 38. The mobile station of claim 35, whereinthe origination functions include sending an Enhanced OriginationMessage wherein a data-ready-send (DRS) bit is set to one or zero. 39.The mobile station of claim 35, wherein the origination functionsinclude sending an agent solicitation to solicit a response from thesecond PDSN.
 40. The mobile station of claim 39, wherein the originationfunctions further include terminating or renegotiating PPP(Point-to-Point Protocol) if no response to the agent solicitation isreceived by the mobile station from the second PDSN.
 41. The mobilestation of claim 39, wherein the origination functions further includeconsulting the database to determine whether an IP address received fromthe second PDSN in response to the agent solicitation matches an IPaddress of the first PDSN stored in the database.
 42. The mobile stationof claim 41, wherein the origination functions further includerenegotiating PPP (Point-to-Point Protocol) if the received IP addressmatches the IP address of the first PDSN.
 43. A mobile stationconfigured to maintain packet data connectivity in a wirelesscommunications network, the mobile station comprising: a changedetection mechanism configured to detect a change from a first packetcontrol function (PCF) to a second PCF, the first PCF corresponding to afirst packet data service node (PDSN), the second PCF corresponding to asecond PDSN; a database consulting mechanism configured to consult adatabase, the database being configured to map at least one previouslyvisited PCF to a servicing PDSN; and an origination pattern responsemechanism configured to cause the mobile station to observe at least oneorigination pattern from among a plurality of predetermined originationpatterns, based at least in part on the consulting, wherein anorigination pattern defines origination functions to be performed by themobile station in order to maintain connectivity within the network. 44.The mobile station of claim 43, wherein the database consultingmechanism is configured to determine at least one of: whether the secondPCF was previously visited by the mobile station and the second PDSN isthe same as the first PDSN; whether the second PCF was previouslyvisited by the mobile station and the second PDSN differs from the firstPDSN; and whether the second PCF was not previously visited by themobile station.
 45. The mobile station of claim 43, wherein theorigination functions include at least one of reregistering mobile IPand renegotiating PPP (Point-to-Point Protocol).
 46. The mobile stationof claim 43, wherein the origination functions include sending anEnhanced Origination Message wherein a data-ready-send (DRS) bit is setto one or zero.